The invention relates to a catheter: with a cylindrical vascular support made of a permeable mesh of crossed stiff fibers, in which the vascular support, when inserted, expands on its own by means of its radial elasticity from a taut state with a small circumference into a relaxed state supporting the vascular wall with a consistent circumference over the entire length; with a tubular outer catheter shaft which receives the taut vascular support at its distal end and from which the vascular support can be released for insertion; and with an inner catheter inside the tubular outer catheter shaft which can be slid within the outer catheter, which is supported along its length for direct conveyance of the sliding routes in the outer catheter and which leaves a passage free in its interior for a guide wire, which it tightly encloses; in which the outer catheter shaft is drawn back with respect to the inner catheter to release the vascular support; in which the vascular support is secured at its proximal end when clamped in such a way that it forms, together with the vascular support, a self-opening permeable mesh cone, the radius of which steadily increases to the size of the radius of the relaxed vascular support; and in which the vascular support, with the aid of the mesh cone, is firmly anchored to the inner catheter, which transmits only compressive and tensional forces.
Catheters of this type have a vascular support at their distal end which is only inserted into the body temporarily in order to support a vascular wall during a specific period of time. After that, the vascular support is to be removed from the vessel.
Vascular wall supports that remain permanently in the body are used, for example, after balloon dilation of a coronary vessel. A main complication in this technique consists of the fact that, as a result of the forcible expansion of the blood vessel, part of the intima, the innermost layer of the vascular wall, can separate from the vascular wall and can then hinder the flow in the vessel to a greater or lesser extent. In the worst case, a separated section of the vascular wall can act like a valve flap, which completely blocks the flow. At specific treatment sites, for example, precisely in the coronary arteries, this leads to a critical situation, which makes an emergency bypass operation necessary with high risk to the patient. However, even at other treatment sites and in the case of a less unfavorable course of complication, this effect, at any rate, prevents the success one seeks to achieve with the treatment.
For some time, therefore, in the case of such complications, the vascular support known from U.S. Pat. No. 4,655,771, for example, have been inserted into the vessel at the site to be treated in order to keep the vessel open from the inside.
For this purpose, using the same puncture that has already been used for the balloon catheter, a catheter is introduced into the blood vessel. The vascular support is cylindrical and consists of a mesh of crossed stiff fibers. It is self-expanding, i.e., it is inserted into the catheter in the taut state and then relaxes on its own without assistance. Other types of vascular supports have to be expanded, e.g., by means of an internal balloon. At the treatment site, the vascular support is released and separated from the catheter by drawing back the outer catheter. A sliding inner catheter located within the catheter serves as a support for the vascular support while the outer catheter is pulled back. After its release, the vascular support remains in the vessel and supports the vessel permanently. The catheter, on the other hand, is withdrawn in the usual manner and the vessel puncture site is closed.
Vascular supports of this type fulfill their purpose to the extent that they press the separated, innermost vascular layer, the intima, back against the vascular wall and thus keep the vessel open for flow. However, problems arise insofar as these vascular supports can cause blood clots, since they represent foreign bodies in the vessel. This danger must be counteracted with high, potentially dangerous doses of anticoagulant agents. After several weeks, the vascular support is then overgrown by the inner skin of the vessel, the endothelium, and the danger of blood clots is thereby largely averted. Now a new problem arises. This is namely because the tissue cells, the growth of which was stimulated by the introduction of the vascular support, do not stop growing in some cases. A new partial or complete occlusion of the vessel can therefore occur.
However, it has become known in the meantime that a separated intima can be reconnected to the vascular wall and healed within a relatively short time. In some cases, all that is required is another brief filling of the balloon at the end of the balloon catheter described. While the balloon is stretched, however, blood flow is interrupted in the vessel in question. This method therefore cannot be used at all treatment sites. In addition, the healing times are prolonged by anticoagulant drugs that may be necessary during the treatment. In this case, the blood supply would accordingly have to be interrupted for a longer period if one wanted to press the intima against the vessel wall by means of a balloon.
In order to avoid the problems described, catheters have therefore already been proposed in which the vascular support can be removed from the vessel. In this case, no implant remains in the body and the complications related to this do not occur. As soon as the vascular support has fulfilled its task and the intima has been reconnected to the vascular wall, this aid can be removed from the body.
An example of this is described in European patent application 0 321 912 A1. It involves a vascular support consisting of a longitudinally stretched mesh tubing made of interwoven wires which is introduced into the vessel in its stretched state. At the treatment site, the two ends of the mesh tube are moved towards each other. As a result, the mesh between the ends bulges into a hollow form which lays against the inner wall of the vessel and supports it. The mesh from which the vascular support is made thus is not self-expanding in this case, but rather is relaxed in the stretched state. In this relaxed stretched state with a small circumference, the vascular support is introduced into the vessel and is then removed from the vessel after use. The strength of the pressure the hollow form exerts on the vascular wall depends on the degree of force with which the ends of the mesh tube are moved towards each other. However, a disadvantage of this design is that the individual wires can kink if the ends of the mesh tube are drawn toward each other with too much force, and the wires cannot move out of the way in the vessel. With kinked wires, the catheter can be removed from the vessel only with complications, because the actuating elements of the mesh can transmit compressive forces only to a limited extent in order to return the mesh to its stretched state with a small circumference. Another disadvantage is the fact that the actuating forces for keeping the mesh tube open for the length of treatment must be maintained from the outside over a relatively long distance. In this case, transmission failures can occur if, for example, the catheter is moved between the skin puncture and the treatment site.
Another example for a vascular support that can be removed from the body is shown in World Patent Application 91/07 928. In this case, the vascular support is made from a helically wound single wire. The wire is inserted stretched into a thin catheter tube and is pushed forward out of this. As soon as the wire emerges from the front of the thin catheter tube, it takes on a spiral or helical form, because of its designed tension. The individual turns of the helical form push outward radially and support the vascular wall. To remove the vascular support, the wire is drawn back into the catheter. In this process, the wire again reassumes its stretched form. This vascular support is therefore self-expanding. With the self-expanding type of vascular supports there is no threat of the danger that excessive operating forces will impair the vascular support or make it unusable. However, the use of only a single wire is accompanied by the disadvantage that the individual turns of the vascular support must be arranged very close together in order to support the surface of the vascular wall and therefore be effective. In addition, in a helical form with only one wire, the turns are not connected to each other, so that there is nothing to keep the distance between the turns uniformly close. Gaps in the support of the vascular wall can thus develop. Another unpleasant disadvantage is the fact that the helical vascular support does not remain stationary during insertion and removal from the vessel. During the insertion and removal of the vascular support, each relaxed part of the helical spring must rotate with respect to the wire in the catheter in order to compensate for the different state of the wire. During placement of the vascular support, the free, rotating end of the wire can cause damage to the vascular wall in this process. Primarily, however, during insertion, the helical vascular support can move below a separated flap of the vascular wall as a result of its rotation and can thus prevent the fulfillment of its task. The action of this vascular support is therefore not as reliable as, for example, that of the known vascular support that remains permanently in the vessel. Problems can also result from the fact that, at the proximal end of the catheter, the total force for ejecting the vascular support must be transmitted by means of only one wire.
Another example of a vascular support that can be removed from the vessel has been published in European Patent Application 0 423 916 A1. This involves a slidable screen made of stainless steel wire and assembled in the form of a section of tube jacket. This vascular support is also self-expanding and, just like the vascular support according to U.S. Pat. No. 4,655,771, is inserted into the vessel by drawing back an outer catheter with respect to an inner catheter. At the close, proximal edge of the slidable screen that has been assembled into a tube jacket section a thread is attached at the edge of the tube jacket. With this thread, the tube jacket can be tied together at its proximal end. In order to achieve this, both ends of the thread are guided out of the body and are loosely secured there while the vascular support is in the vessel. If the vascular support is to be removed, a new catheter is fed over these two threads up to the vascular support and the proximal end of the support is tied together by pulling on the threads. Then a second, correspondingly larger catheter is pushed over the first. The vascular support is now pulled together with the threads far enough until it fits into the larger catheter and can be drawn into it. After this, both catheters, together with the vascular support, are removed. The disadvantage of this arrangement is the large effort it requires. The operation is very cumbersome because of the handling of the threads and the placement of at least one new catheter, which, for example, must also be pushed over the threads. A large number of instruments is also required, and at least one additional catheter must be provided that will receive the vascular support. The catheter used for placement of the vascular support is too small for this purpose. In inserting the vascular support into the coronary arteries, difficulties are also to be expected when drawing the vascular support into the larger catheter, because the coronary arteries are in constant movement. The difficulties then arise due to the fact that the vascular support, which is drawn together at the proximal end, does not always lie exactly in the center of the larger catheter and the vascular support also does not center itself with respect to the larger catheter. The vascular support remains hanging at the edge of the larger catheter.
The catheter with a vascular support, constituting the preamble of the claim, became known after the filing date of European Patent Application 92 200 294.4 and corresponds to the description given there.
In this catheter, a self-expanding vascular support according to U.S. Pat. No. 4,655,771, made of a permeable mesh of crossed fibers is anchored in a folded and inserted state to an inner catheter at the proximal ends of the mesh fibers. While the catheter is fed into the vessel, the vascular support is supported in the inserted state in a corresponding outer catheter. As soon as the outer catheter is withdrawn with respect to the inner catheter, the vascular support will emerge distally from the outer catheter and relax. Due to the fact that it is anchored to the inner catheter in a folded state, a mesh cone is formed at the proximal end of the vascular support in the relaxed state. The conical form of the mesh and its anchoring to the inner catheter make it possible for the vascular support to be reliably folded back into the outer catheter after use by advancing the outer catheter and thus to remove it from the vessel.
This catheter corresponds largely to the demands made on it, but a still unsatisfactory factor with regard to this catheter is the phase during the course of the operation where the taut vascular support is located within the outer catheter and the catheter is fed into the vessel. In this phase, the outer catheter must be closed by means of a protective cap. Otherwise, the outer catheter would load up with the respective body fluid when it was fed into the vessel. Primarily, the vascular wall would then be directly exposed to the advancing edge of the distal outer catheter opening. Injuries can be caused as a result. To prevent injuries in general when feeding a catheter into a vessel, a guide wire is normally inserted, which guides the catheter from the inside and over which the catheter is advanced. In the catheter under discussion in the present case, the insertion of a guide wire cannot permanently eliminate the danger of injury. On the one hand, a guide wire must be as thin and flexible as possible and, in any case, the possibility of injuries caused by the guide wire itself must be ruled out with certainty. The distal opening of the outer catheter, through which the guide wire rubs, on the other hand, must be many times larger than the diameter of the guide wire, because it must receive the vascular support. Because of the large difference in diameter between the guiding element on the one hand and the element to be guided on the other hand, a guide wire cannot conduct this catheter with the required safety and thus prevent the possibility of injuries. The protective cap, which is provided at the distal end of the catheter, also presents problems. On the one hand, it should close the distal outer catheter opening reliably in the closed state and protect the vascular wall reliably against injuries. On the other hand, however, it should, if possible, not offer any resistance to the withdrawal and the folding in of the vascular support. It is difficult to satisfy both requirements at the same time. Primarily, however, difficulties are to be expected in folding the vascular support back into the outer catheter in the case of vascular supports made from a wide mesh net. In addition to the tasks described above, the protective cap cannot also guide the catheter along the guide wire. This would contradict the requirement that the cap must also permit easy withdrawal of the vascular support. The guide wire in this catheter therefore has practically no perceptible guidance and is uncontrolled in the much larger distal opening of the outer catheter.